The invention relates to rotary mechanisms, particularly to rotary compressors or expansion engines in which the rotor has a planetary motion within a housing and the peripheral surface of the rotor is substantially a hypotrochoid and the inner surface of the housing is substantially the outer envelope of the relative rotary motion of the rotor. Such a compression or expansion engine is disclosed in U.S. Pat. No. 3,387,772 granted June 11, 1968 to Wutz and in British Pat. No. 583,035 granted Dec. 5, 1946 to Maillard and is generally known as a Maillard-type compressor. The invention will herein be described in terms of compressor operation although as will be apparent it is also applicable to expansion engines.
Various trochoidal compressors have been proposed in the past in which either the outer periphery of the rotor or the inner periphery of the rotor housing is a trochoidal surface, either an epitrochoid or a hypotrochoid. For example, U.S. Pat. No. 3,671,153 granted on June 20, 1972 to Luck shows a compressor in which the inner surface of the rotor housing is an epitrochoid. Similarly, U.S. Pat. No. 3,452,643 granted July 1, 1969 to Pratt shows an expansion engine in which the inner surface of the rotor housing is an epitrochoid. A rotary mechanism having the geometry of the rotor and rotor housing shown in the Luck and Pratt patents is generally known as a Wankel-type rotary mechanism. It has been determined that a Maillard-type compressor has the advantage in that the minimum volume of each working chamber is reduced substantially to zero at the end of the discharge stroke of each working chamber thereby providing a compressor with relatively high volumetric efficiency.
The efficiency of a rotary compressor depends on the provision of adequate sealing for each working chamber. In a Wankel-type configuration it is difficult to provide adequate sealing between the rotor peripheral surface and the waist portions of the rotor housing because these waist portions do not generate the peripheral surface of the rotor, although in a Wankel-type configuration a seal bar can readily be provided at each apex portion of the rotor because each apex portion generates the epitrochoid inner surface of the rotor housing. However, a seal bar cannot readily also be provided at the waist portions of the rotor housing in a Wankel-type configuration particularly because of possible mechanical interference with the apex seal bars on the rotor.